I. Title of the Invention
The present invention concerns a spinning method for performing spinning to the end part of a work piece in a non-circular cylindrical shape or, more preferably, a work piece in an elliptical shape including an ellipse and a flat part, and an apparatus for implementing such a method.
II. Description of Related Art
FIG. 7 through FIG. 9 illustrate an example in which spinning was performed by a conventional method on a work piece W in a non-circular cylindrical shape, a work piece in an elliptical shape for example, to manufacture a muffler 50 for an automobile.
This working method consists of forming an end part of the work piece W in an elliptical shape into an inclined face 52 inclined in a way so as to have a gradual reduction in diameter, and performing spinning, for forming a certain length of the end part into a circular cylindrical shape 51 with a prescribed diameter, to both end parts of the work piece W, to make the work piece W into a product 50 (muffler for automobile).
When this conventional working method is employed, a swollen part b is produced, as shown in FIG. 9, in a region near the minor axis a of the work piece W, because the roller does not come into contact with that region at the time of spinning and the pads of the work piece W in the surrounding area gather in that region. A problem was that this swollen part b not only spoils the appearance of the product 50 (muffler for automobile) but also has negative influences on the product performance.
To cope with this problem, the present applicant proposed, previously, a spinning method of a work piece in a non-circular cylindrical shape realized in a way to eliminate the swollen part b for solving this problem, by performing spinning to the swollen part b produced in a region near the minor axis a of the work piece W (see Japanese Laid-open Patent Application No. 2001-257256).
This working method consists in forming, as shown in FIG. 10 to 11, an end part of the work piece W in an elliptical shape into an inclined face 33 inclined in a way so as to have a gradual reduction in diameter, and moving the work piece W, which has been submitted to spinning for forming a certain length of the end part of the work piece into a circular cylindrical shape 32 with a prescribed diameter, in the radial direction of a minor axis (upward in FIG. 10 to 11) of the work piece W, setting the working locus A′ of the spinning roller R at a radius close to the curved surface of the minor axis 31 of the work piece W, and forming a formed face 34 by performing spinning in the state in which, at least, the unworked part (part with which the roller did not come into contact at the time of spinning in the preceding process) of the minor axis 31 is positioned on the spinning roller R side with reference to the working locus A′ of the spinning roller R, to make the work piece into a product 30 (muffler for automobile) without the swollen part b.